Exclude this and reformat the toml option to multiline.

I wasn't able to get `exclude_regex` to work so it would include a
`tests` directory anywhere. I think that option only works on files.

### Before

```
$ make watch
bash build/watch.sh
make[1]: Entering directory '/Users/silverwind/git/gitea'
make[1]: Entering directory '/Users/silverwind/git/gitea'
GITEA_RUN_MODE=dev go run github.com/cosmtrek/air@v1.43.0 -c .air.toml
rm -rf public/js public/css public/fonts public/img/webpack public/serviceworker.js
NODE_ENV=development npx webpack --watch --progress
```

### After

```
$ make watch
GITEA_RUN_MODE=dev go run github.com/cosmtrek/air@v1.43.0 -c .air.toml
NODE_ENV=development npx webpack --watch --progress
```

Current air version runs the old binary if the build fails. This
restores the old behaviour.

```
...
code.gitea.io/gitea/services/cron
code.gitea.io/gitea/routers/web/user/setting
code.gitea.io/gitea/routers/web/org
make[2]: *** [Makefile:814: gitea] Error 1
make[2]: Leaving directory '/src'
failed to build, error: exit status 2
running...
2023/04/30 21:04:11 cmd/web.go:125:runWeb() [I] Starting Gitea on PID: 29153
2023/04/30 21:04:11 cmd/web.go:178:runWeb() [I] Global init
...
```

Reference: https://github.com/cosmtrek/air/pull/336

https://github.com/cosmtrek/air/pull/343 has changed air's default
`delay` from 1000 to 0 and since then, while switching git branches, I
notice air starting off multiple parallel build, essentially overloading
my machine. Restore previous value of 1000.

````
building...
routers/web/org/setting_secrets.go has changed
routers/web/org/teams.go has changed
building...
routers/web/org/teams.go has changed
routers/web/repo/setting_secrets.go has changed
building...
routers/web/org/setting_secrets.go has changed
routers/web/repo/setting_secrets.go has changed
building...
routers/web/shared/secrets/secrets.go has changed
routers/web/repo/view.go has changed
building...
routers/web/repo/view.go has changed
routers/web/user/setting/secrets.go has changed
building...
routers/web/shared/secrets/secrets.go has changed
routers/web/user/setting/secrets.go has changed
building...
routers/web/web.go has changed
routers/web/web.go has changed
building...
services/wiki/wiki_path.go has changed
services/wiki/wiki_path.go has changed
building...
...
Running go generate...
Running go generate...
Running go generate...
Running go generate...
Running go generate...
Running go generate...
Running go generate...
Running go generate...
Running go generate...
Running go generate...
Running go generate...
Running go generate...
Running go generate...
Running go generate...
Running go generate...
```

- Update all tool dependencies to latest tag
- Remove unused errcheck, it is part of golangci-lint
- Include main.go in air
- Enable wastedassign again now that it's
[generics-compatible](https://github.com/golangci/golangci-lint/pull/3689)
- Restructured lint targets to new `lint-*` namespace

Since #20218 introduced internal watching template, template watching
should be removed from `air`. This will prevent restart the whole server
once the template files changed to speed up developing when using `make
watch`.

To ensure `make watch` will reuse template watching, this PR introduced
a new ENV `GITEA_RUN_MODE` to make sure `make watch` will always run in
a dev mode of Gitea so that template watching will open.

This PR also added more exclude testdata directories.

- Don't rebuild the binary when generated files are updated, which is the
case by-default when running `make watch`.

As of https://github.com/cosmtrek/air/pull/90, the preferred file
extension is .toml. The file format was always toml itself.

* Add 'watch-backend'

This leverages `air` to watch the backend files and trigger `make
backend` automatically when they change. It seems to work rather well
together with `watch-frontend`.

Fixes: https://github.com/go-gitea/gitea/issues/12318

* rework docs to a new section for continuous build

Co-authored-by: techknowlogick <techknowlogick@gitea.io>